Aerodynamics [Archive] - Honda Ridgeline Owners Club Forums

: Aerodynamics


Kodiak
03-07-2007, 06:41 AM
Here are excerpts from an article published by Edmunds. This is public domain information which I can share. The full article can be found at the following web address: http://www.edmunds.com/advice/specialreports/articles/106954/article.html

I can not share the exact coefficient of and drag and frontal area (CDA) for the Ridgeline. I can however say that it is the most aerodynamic truck on the market today – bar none. It however is not a passenger car. Passenger cars have significantly less frontal area and much lower CD. They also do not have sufficient cooling to tow a large trailer. Read the excerpts from the following article and you will perhaps have a better understanding of the positive and negative influences on aerodynamics.


How Drag Affects Mileage
When you consider aerodynamics from a fuel economy standpoint, you're primarily looking at coefficient of drag (known in the business as "Cd"). Essentially, this is how easily a vehicle moves through the air, though drag isn't the only factor that is considered. "There's more to aerodynamics than just drag," says Doug Frasher, strategic design chief at the Volvo Monitoring & Concept Center. "There's downforce and lift. And there is yawing moment, which is basically when you're in a crosswind, how much does the vehicle get steered by the wind that is pushing on it? And then there's noise. So we try to look for all of those factors.

"For a full-size truck, a change in drag coefficient of 0.01 is approximately equal to an improvement in fuel economy of 0.1 mpg on the combined city/highway driving cycle," says GM's Schenkel. "The same drag coefficient reduction can improve a car's fuel economy by approximately 0.2 mpg."

Volvo's Frasher says the force acting against a car by the air it moves is a function of:

Cd x Frontal Area x Density of Air x Speed Squared

Speed clearly is an important part of the equation. At stop-and-go speeds, drag isn't a big deal, but the faster you go, the more it matters. At 70 mph, you've got four times the force working against your vehicle that you have at 35 mph.

To put Cd changes in perspective, Frasher put some numbers to a hypothetical sedan. Our imaginary car has a curb weight of 3,527 pounds, a Cd of 0.30, a frontal area of 23.7 square feet and 9 pounds of rolling resistance for every 1,000 pounds of weight.
According to Frasher, "If we put a gas-burning engine in this car, expect reasonable performance and drive it on a combined driving cycle, we can expect to get 23.8 mpg…. Add 10 percent to the drag coefficient, we'll now get 23.3 mpg…. Take 10 percent from the drag coefficient, we'll now get 24.3 mpg."

Cars typically have a much lower Cd than pickups and SUVs, which sit higher, are bigger and have greater cooling needs. Cooling is a big deal, aerodynamically speaking, since it requires airflow into the vehicle through the radiator, which increases drag.

Steve Wegryn, manager of Ford Motor Co.'s aerodynamics department, says, "For trucks, we're anywhere in the range of 0.40 to 0.43, 0.44…. For cars, on the order of 0.30 to 0.34. And SUVs are somewhere in between 0.36…to…0.41."

How to Improve the Aerodynamics of Your Car
Automakers spend a lot of time optimizing vehicles' aerodynamics. But is there anything we can do to improve — or at least not degrade — the aerodynamics of our own vehicles?

It turns out the biggest gains are to be found on pickups — not by dropping the tailgate (a common misconception), but by installing a tonneau cover. "A tonneau cover improves the aerodynamics dramatically — on all pickup trucks," according to Ford's Wegryn. "In general, a tonneau cover can provide a drag reduction of 2 to 7 percent, depending on cab style, box length and overall vehicle Cd. Average fuel economy improvement ranges from 0.1 to 0.3 mpg." From an aero standpoint, it doesn't make a difference if you choose a soft or hard cover.

You'll also improve aerodynamics by:
Reducing the use of roof racks
Rolling up your windows and turning on the air conditioner at higher speeds, typically above 35 mph
Replacing a broken or missing front air dam
Lowering your vehicle
Running narrower tires
Choosing smoother wheels (ideally, flush discs like those on vehicles trying to set land speed records)
You can reduce your vehicle's aerodynamics by:
Lifting it — "an inch of increased ride height degrades the coefficient of drag by about 10 drag counts [.01]," says Wegryn.
Adding wider tires
Choosing more "open" wheel designs (although, for many owners, this advantage will be offset by the fact that "open" wheels promote better brake cooling)
Installing a bug shield
Adding a rear spoiler, in some cases
As a rule, an increase in noise is a sign of increased drag that is reducing your aerodynamics.

K

zero
03-07-2007, 09:32 AM
Excellent article, Kodiak.

Good to see you back on the boards and posting.

Kodiak
03-07-2007, 10:24 AM
Lesson 2:

Affect of Air Temperature on Drag
Based on the ideal gas law, the following is the cold weather impact on drag force which is a partial explanation for a drop in fuel economy during the winter months. The results are using 25 degrees Celsius and 65 mph speed as a base conditions. Curves are shown at higher speeds also indicating the impact of speed in addition to temperature. All numerical values are percentage relative reverences to that base condition:

(See Chart Below)

As you can see from this comparison, a drop in ambient temperature from 25C to 0C results in an approximately 10% increase in drag force. If you combine this effect with increased speeds, comparing 65mph at 25C to 75mph at 0C results in 45% increase in drag force.

In conjunction with the reduced energy content in “winter” fuel blends, and the increased time spent at higher air-fuel ratios due to cold start conditions, both issues contribute to the climatic impact cold weather has on fuel economy.

K

Kodiak
03-07-2007, 11:26 AM
Lesson 3: Fuel Variations

Winter fuel is formulated in northern climates to improve cold start performance. This fuel has an adverse affect at elevated temperatures which is why there are seasonal blends of gasoline (as you may recall, you can experience “vapor lock” from winter grade fuels at elevated temperatures). Typically, winter fuels have been reported to negatively impact fuel economy by approximately 2%. This represents about a 0.5 mpg reduction in fuel economy on its own. You might believe you are insulated from this type of issue because you live in a warmer climate. There are many different fuel blends regulated by the EPA due to environmental considerations (see chart below).

The EPA requires reformulated gasoline (RFG) in a number of ozone-nonattainment areas. Federal RFG must be oxygenated year-round to 2.1 percent by mass oxygen, average. In addition, the EPA requires gasoline in some carbon monoxide-non-attainment areas to be oxygenated during the winter months to a minimum of 2.7 percent by mass oxygen. Finally, California's Air Resources Board (CARB) requires a different RFG throughout California. California RFG must be oxygenated year-round in those areas where federal RFG also is required. A recent regulatory change eliminated the requirement for oxygenated RFG in most other areas of California.

Based on several studies, RFG fuel have also been shown to negatively impact fuel economy by approximately 2.8% (0.6 mpg reduction in fuel economy).

There are many different gasoline blends that vary greatly by geographic location. The fuel variations combined with the climatic variables affecting aerodynamic drag, driving cycle and fuel mixture, results in many complex variables that negatively impact fuel economy. This is why you experinece a reduction in fuel ecoomy during the winter months.

nevadagarth
03-08-2007, 11:21 AM
KODIAK!! Welcome Back!

It is always refreshing to have someone post on here who actually knows what they are talking about.

rms56
03-08-2007, 12:24 PM
Great info!!! Now if you tack on vehicle warm up time as part of a winter routine you really reduce your mileage. Winter conditions are the primary reason that I swtched to Mobile 1 for my RL. Better cold start lub and less warm up time.